1. Field of the Invention
The present invention generally relates to an LSI package, and particularly relates to an LSI package including an LSI device operating at a higher clock frequency.
Recent LSI devices tend to operate at higher frequency and with higher electrical consumption. Accordingly, there is a need for packages for mounting the LSI devices thereon, or LSI packages, which can be used with such LSI devices. Thus, the LSI packages are modified as follows.
First, in order to stabilize an electric current supply, the LSI package is formed in a multilayer structure with an inner layer provided with a source/ground plane. Secondly, in order to reduce an inductance of source/ground lines, the source/ground lines are provided so as to be short in length and broad in width. Thirdly, in order to achieve a 50 .OMEGA. impedance matching, gaps between layers are adjusted by providing planes on layers above and below wiring layers. Finally, in order to reduce mutual inductance and crosstalk, gaps between signal lines are widened so that the signal lines do not interfere with each other.
2. Description of the Related Art
Now an LSI package of the related art will be described in detail with reference to FIGS. 1 and 2. An LSI package 1 shown in FIGS. 1 and 2 is a double-layer package including an upper layer 2 (shown in FIG. 1) and a lower layer 3 (shown in FIG. 2). FIGS. 1 and 2 show 1/8 of the whole pattern of the LSI package 1.
As shown in FIGS. 1 and 2, through-hole lands 4 are formed in a matrix form on both the upper layer 2 and the lower layer 3. The through-hole lands 4 are connected to external terminals via through-holes. The external terminals are provided with, for example, bumps. With the structure described above, the LSI package 1 may be used as a BGA (Ball Grid Array) type package.
Also, the upper layer 2 and the lower layer 3 are provided with a number of lines 5. Each of the lines 5 is connected to one of the external terminals via a through-hole at one end, and to an electrode pad 6 on the other end. The electrode pads 6 are formed on the upper layer 2 and the lower layer 3 at positions facing a semiconductor chip (not shown). The electrode pads 6 are electrically connected to the semiconductor chip using wires.
Now, the lines 5 will be described in detail. In the related art, the relationship between the lengths of the lines 5 on either the upper layer 2 or the lower layer 3, or the lines 5 on both the upper layer 2 and the lower layer 3, was not of a great interest. The wiring pattern was determined so as to facilitate the forming process of the lines 5.
However, for source lines and for ground/source lines, which are labeled a-g in FIGS. 1 and 2, the line lengths were shortened for the sake of electrical feature and the line widths were broadened as shown by the line labeled g in FIG. 2. Also, impedance matching was achieved by a multilayer package provided with a signal-transmitting layer held between the source planar layer and the ground planer layer.
In the related art, improvement of electrical characteristics of the LSI package 1 has focused on improvement of the LCR characteristics or the 50 .OMEGA. matching of the characteristic impedance according to the modifications described above. Thus, the LCR characteristics, the impedance matching of the LSI package, and crosstalk problems have been improved. However, there is still a need for reducing the noise produced by the mismatch of transmission times between differential signals.
Also, when the above-described modifications are applied to the recent LSI devices having a clock frequency of over 1 GHz, there is a problem that when the LSI device is mounted on the LSI package 1, the LSI device (semiconductor device) does not operate.